Traditional methods for obtaining salt-spray resistance of unpainted metal, such as high copper-containing aluminum alloys, without affecting adhesion of the top coat include conversion coating with hexavalent chrome solutions and the applications of solvent-base wash primers that contain insoluble chromate pigments and phosphoric acid--see, for example, "Encyclopedia of Chemical Technology", Kirk-Othmer, Volume 9, pages 14-17 (1952); "Metals Handbook", 9th Edition, Volume 5, pages 597-600 (1982); "Preparation of Metals for Painting", Samuel Spring, pages 94-96 and 142-158 (1965). Increasingly stricter hazardous waste restrictions have now placed limits on the use of such toxic chromium salts. Thus, the industry is in need of alternative protective coatings which will enable the unpainted metal to withstand 168 hours salt-spray attack.
Copending application Serial No. 735,481, filed Jul. 25, 1991, discloses formulations based on aqueous emulsions of acrylic polymers, but the instant solutions or dispersions enable good corrosion resistance and paint adhesion properties to be obtained at far less cost.